Unit 08 - Modeler¶
Graphical Modeler allows creating, editing, and managing complex models in easy-to-use graphical user interface. Using Graphical Modeler a chain of processes (ie. GRASS modules) can be wrapped into one process (a model). A model can be executed repeatedly with slightly different inputs or parameters.
Our first model will be based on Unit 05 - Simple computation. Actually the model will perform two operations:
Graphical Modeler can be launched from menu Graphical Modeler
from main toolbar (or alternatively as g.gui.gmodeler
module from console).
![../_images/gmodeler.png](../_images/gmodeler.png)
Fig. 59 Graphical Modeler.
GRASS modules can be added to the model from menu
Add command (GRASS module) to the model from main toolbar.
![../_images/add-module.png](../_images/add-module.png)
Fig. 60 Add commands (GRASS modules) to the model, in this case r.mask.
After adding r.mask module to the model let’s open its properties dialog by double-click and enter vector map to be used as a mask. Don’t forget to enable inverse mask by -i flag.
![../_images/module-props.png](../_images/module-props.png)
Fig. 61 Define parameters for r.mask, a vector map used for creating a mask.
In similar way will be added to the model the second command i.vi (properties dialog for this command is open automatically because there are required options which must be set).
![../_images/model-v1.png](../_images/model-v1.png)
Fig. 62 NDVI model version 1.
It’s good idea to set metadata for the model and enable overwriting data produced by model (
).Fig. 63 Define model properties and enable overwriting data produced by model.
Such model can be run repeatedly using different computation regions.
Tip
Current computation region can be changed quickly by Set
computation region extent interactively from
Various zoom options in Map Display.
![../_images/model-v1-region.png](../_images/model-v1-region.png)
Fig. 64 Change computation region before running the model.
Important
Before changing the region it’s good idea to remove mask if exists from r.mask module).
(byr.mask -r
Now let’s run our model by Run model. Progress
is printed into Command output.
![../_images/model-v1-output.png](../_images/model-v1-output.png)
Fig. 65 Model computation progress.
After redrawing map display Render map (assuming
that we have already displayed raster map of NDVI in map display), we
should see a difference.
![../_images/model-v1-display.png](../_images/model-v1-display.png)
Fig. 66 New NDVI raster map computed by the model.
Sample model to download: ndvi-v1.gxm